Seven days for a feast was the customary period for observing a religious festival in Israel; see, for example, Exodus 12:15; Leviticus 8:33; Leviticus 23:34; 1 Kings 8:65; Ezekiel 43:25). This may also have been the customary length of a marriage feast; at the very least, it is likely that the seven days of Samson’s marriage feast followed the established practice in Timnah.
12 And Samson said to them, “Let me now put a riddle to you. If you can tell me what it is, within the seven days of the feast, and find it out, then I will give you thirty linen garments and thirty changes of clothes,